Solution to DNS resolution CNAME configuration error

　　In website deployment and domain name resolution, CNAME records are a DNS configuration method that almost every website owner will encounter. Especially when using CDN, cloud servers, object storage, or third-party platforms, CNAME is indispensable. However, in reality, many problems such as inaccessible websites, abnormal subdomains, and expired SSL certificates often trace back to incorrect CNAME configurations.

　　I. What is a CNAME Record? Why is it so important?

　　CNAME is usually called an "alias record." Simply put, it points one domain name to another.

　　For example: You have a domain name www.example.com

　　Your service provider requires you to CNAME it to:

　　example.cdnprovider.com

　　At this time, when accessing www.example.com, the DNS will continue to resolve to the IP address corresponding to example.cdnprovider.com.

　　Unlike A records, which directly point to an IP address, CNAME points to a domain name. The advantages of this method are:

　　First, it avoids frequent IP changes; only the service provider needs to adjust the target domain name.

　　Second, it facilitates CDN, load balancing, and multi-node scheduling. Third, it is suitable for dynamic architectures such as cloud services, object storage, and SaaS platforms.

　　However, precisely because of this "secondary resolution" characteristic, improper configuration can easily lead to various access anomalies.

　　II. Typical Manifestations of CNAME Configuration Errors

　　In actual operation and maintenance, CNAME problems typically manifest in the following ways:

　　The website is completely inaccessible, with the browser displaying DNS_PROBE_FINISHED_NXDOMAIN.

　　Only the main domain can access it; www or subdomains cannot be opened.

　　HTTPS certificate errors or ineffectiveness.

　　The CDN console displays "not connected" or "origin return error."

　　Accessible in some regions, but resolution fails in others.

　　Ping the domain name yields no response, but pinging the target domain name is normal.

　　If you encounter any of the above situations, you should first suspect whether the CNAME configuration is correct.

　　III. Common CNAME Configuration Errors Made by Beginners

　　1. Configuring both CNAME and A records under the same hostname.

　　This is one of the most common problems.

　　For example: www.example.com contains:

　　A record → 1.2.3.4

　　CNAME → example.cdn.com

　　The DNS specification clearly states that the same hostname cannot simultaneously contain CNAME and other record types.

　　The solution is simple: choose one. When using a CDN or third-party platform, delete the existing A record and only keep the CNAME.

　　2. Use CNAME directly for the root domain

　　Many beginners try to add a CNAME to example.com (the bare domain). However, most DNS providers do not support root domain CNAMEs because the root domain usually also carries critical records such as NS and SOA.

　　There are two solutions:

　　Use the "ALIAS" or "ANAME" function provided by the service provider.

　　Configure only a CNAME for www, then redirect the main domain to www using a 301 redirect.

　　This is currently the most reliable and compatible approach.

　　3. Incorrect CNAME target or missing trailing dot

　　For example, if your service provider offers: abc.cdnprovider.com,

　　but you enter: abc.cdnprovider.co, or omit a part of the URL.

　　Even a single incorrect character can cause the DNS resolution to fail completely.

　　It is recommended to directly copy the target address provided by the official provider, and not to enter it manually.

　　4. CNAME loop

　　For example:

　　a.example.com → CNAME → b.example.com

　　b.example.com → CNAME → a.example.com

　　This kind of loop resolution will cause DNS to fail completely.

　　You can use: nslookup, dig

　　to check the complete resolution chain.

　　5. Inappropriate TTL setting causing delayed changes to take effect

　　TTL represents the cache time. If you set it to 86400 (24 hours), even after the error has been corrected, some regions may still continue to use the old DNS record.

　　During the debugging phase, it's recommended to set the CNAME record to 300 or 600. Increase it only after the system is fully stable.

　　IV. Standard Troubleshooting Process (Beginners can follow these steps)

　　When you suspect a CNAME configuration error, check the following in order:

　　Step 1: Log in to the DNS console and confirm if the hostname has a duplicate A record.

　　Step 2: Verify that the CNAME target matches the one provided by your service provider.

　　Step 3: Confirm that CNAME is not used directly in the root domain (unless ANAME is supported).

　　Step 4: Check for multi-level CNAME records or circular references.

　　Step 5: Use command-line tools to test the DNS resolution results and observe whether the IP address is successfully resolved.

　　If you are using a CDN, you also need to confirm in the CDN backend that the domain status is "connected".

　　V. How to Avoid Repeating These Pitfalls?

　　We recommend developing the following habits:

　　Before each modification to the DNS record, take a screenshot or export the current configuration. During the debugging phase, lower the TTL. Copy all target addresses directly from the official documentation. Keep only one record type for each hostname. After modification, use a multi-location DNS resolution tool to check. These seemingly simple steps can prevent more than 80% of DNS incidents.

　　VI. Frequently Asked Questions

　　Q1: How long does a CNAME record usually take to take effect?

　　A1: Theoretically, it takes only a few minutes, but the actual time depends on the original TTL value. If the previous TTL was high, it may take up to 24 hours for a complete global refresh.

　　Q2: www is accessible, but the webpage cannot be opened without www. What should I do?

　　A2: This is usually because the main domain is not correctly resolved. We recommend configuring a CNAME record for www and redirecting the main domain to www using a 301 redirect.

　　Q3: Can multiple CNAME records point to the same target?

　　A3: Yes, different subdomains can be CNAME'd to the same target domain simultaneously.

　　Q4: Can a CNAME record point to an IP address?

　　A4: No. A CNAME record can only point to a domain name, not an IP address.

　　Q5: Why does the SSL certificate become invalid after changing the CNAME record?

　　A5: This is usually because the certificate does not cover the domain name, or the CDN certificate has not been redeployed. Reapplying for or redeploying the certificate will solve the problem.

　　Q6: Why are the DNS resolution results inconsistent between domestic and international servers?

　　A6: This is mostly related to DNS caching, CDN nodes, or ISPs. It is recommended to use multi-location testing tools for comparison.

　　Summary: CNAME may seem like a small option in DNS, but it plays a crucial role in modern cloud architecture, CDN acceleration, and multi-node deployment. Most website access problems are not actually server issues, but rather caused by improper DNS resolution layer configuration.